Protector for electric circuits



Patented Oct. 2, "45

PROTECTOR FOR ILIUI'RIO CIRCUITS Manfredl.nlerknb,st-Lollil,hlo.,alimrtoMcGraw Electric Company, Ilsin,

ration of Delaware memo- Application May 15, 1948, Serial No. 487,418

52 Claims. ((1 ZOO-123) This invention relates to improvements inprotectors for electric circuits. More particularly the inventionrelates to improvements in enclosed protectors for electric circuitsthat comprise a fuse link and a thermal cut-out.

It is an object of the present invention to provide an improved enclosedprotector for electric circuits that comprises a fuse link and a thermalcut-out.

Protectors for electric circuits that comprise a fuse link and a thermalcut-out are desirable because they will open the circuit beforeoverloads can cause injury to the circuit, but will not open the circuitneedlessly. Such protectors have the quick opening of the fuse link onheavy overloads as well as the desirable time lag of the thermal cut-outon lighter overloads. When, in this description, the word "circuit isused, it does not refer to the wiring along but refers also to anyelectrical devices that may be a part of the circuit protected by theseprotectors.

Protectors that have a fuse link and a thermal cut-out all have the samefundamental P p and object, but their form and structure may differconsiderably. The difference in form and structure may be due to spacelimitations as well as to considerations of performance and function.Space limitations in protectors that are used in fuse clips. alreadyinstalled and in use. are standardized; and often present an almostinsurmountable obstacle to the making of an enclosed protector forelectric circuits that comprises a fuse link and a thermal cut-out. Notonly must the protector include an additional means to aive the desiredtime lag, but it must be small enough to fitinto an enclosure intendedfor a fuse link only, and such enclosure is often quite small.

The problem of making enclosed protectors for automotive, aircraft andradio work is particularly difficult, because such protectors must beoperable in cylindrical cartridges that may have outside dimensions assmall as one and one quarter inches in length and one quarter of an inchin diameter. Accordingly, the dimensions of such protectors must r 2very very small; and when it is remembered that those protectors areused to protect power circuits; and. in the case of radio work, circuitsup to two hundred and fifty volts. it is obvious how difficult it is tomake such protectors. In fact, the making of a Mr that prises a fuselink and a thermal cut-out and is small enough to fit into such anenclosure. has been heretofore regarded as impossible. The presentinvention makes pouible such a protectorbyusingaminimumnumberofpartsandbymakin: several of the parts movable. Itis therefore an object of the present invention to provide a protectorfor electric circuits, that is operable in small enclosures, by usina alimited number of parts and by making several of the parts movable.

Protectors for electric circuits that are intended for automotive andaircraft work may be. and usually are, subjected to considerablevibration. Where this is the case, the protector must be constructed towithstand considerable vibration or it will have a relatively shorteffective life. The present invention provides a long lived protectorfor electric circuits by resiliently spacing some of the parts of theprotector away from the inner surfaces of the enclosure. such anmonument is desirable because it absorbs the vibration imparted to theenclosure and minimizes the vibrating done by these parts of theprotector. It is, therefore, an object of the present invention toprovide an enclosed protector for electric circuits wherein some of theparts are resiliently spaced away from the inner surfaces of theenclosure.

In the fuses heretofore used in automotive, aircraft and radio work, thefuse links have been initially spaced away from the inner surfaces ofthe enclosure to insure uniformity of operation of the protector. Thisinitial spacing is often incapable of preventing subsequent contactbetween the link and the inner surfaces of the enclosure, andparticularLv is this true where the fuse link is quite long andsubjected to considerable heat. In such cases, the link may expandsufficiently to cause a portion thereof to touch the inner surface ofthe enclosure, and this touching will disturb the performance andoperation of the protector. The present invention obviates such touchingand thereby insures a uniform performance for the protector. bymaintaining some tension in the link and thereby holding the link nearthe diametric center of the enclosure. This tension is preferably notvery heavy but is sumcient to keep the fuse link from sagging minst theinner surfaces of the enclosure. It is, therefore, an object of thepresent invention to provide an enclosed protector for electric circuitsin which tension is used to prevent contact between the fuse link andthe inner surfaces of the enclosure.

In protectors for electric circuits that have a fuse link and a thermalcut-out, a solder may be provided that loses its holding power whenheated to a predetermined temperature. This solder preferably is spacedam from the terminals of the enclosure by a plurality of heat seneratin:elements. These elements largely retard the flow of heat between thesolder and the terminals, and

thereby minimize the tendency of varying temperatures of the terminalsto ail'ect the temperature of the solder. It is therefore an obiect ofthe present invention to separate the solder from the terminals, of theenclosure by a plurality of heat generatin elements.

It is often desirable in protectors for electric circuits to provide aheat absorbing element that may serve as an arcing contact, because suchan absorber will help extinguish any arcs that may form when theprotector opens the circuit. It can do so because its relatively largemass tends to cool the arc. and such cooling tends to extinguish it. Inthe present invention, a heat absorbing member is used as an arcingcontact and it is also movable. This not only permits cooling of thearc, it fosters drawing of the arc and thereby makes for rapidextinction of the arc. It is therefore an object of the presentinvention to provide an enclosed protector for electric circuits inwhich a heat absorbing element constitutes a movable arcing contact ofthe protector.

In the operation of the present invention, a portion of the protector ismoved to open the circuit. Because of space limitations, it is necessarythat this movement be longitudinal of the enclosure to provide a longarcing gap and a consequent rapid extinction of the arc. It is thereforean object of the present invention to provide an enclosed protector forelectric circuits in which the moving part moves longitudinally of theenclosure to open the circuit.

Other objects and advantages of the invention will become apparent froman examination of the drawing and accompanying description.

In the drawing and accompanying description, a preferred embodiment ofthe invention is shown and described, but it is to be understood thatthe drawing and accompanying description do not limit the invention andthe invention will be defined by the appended. claims.

In the drawing.

Fig. 1 is a partial cross-sectional plan view of the protector embodyingthe invention,

Fig. 2 is a partial cross-sectional elevational view of the protectorshown in Fig. l, and

Fig. 3 is a cross sectional view of modified end for the movable member20.

Referring to the drawing in detail, an enclosure for a protector forelectric circuits can be seen to consist of a cylindrical tube l and endcaps l2 and i4. The tube i8 may be made of any suitable material and maybe of any suitable size. In the very small sizes, for which the presentinvention is particularly useful, the tube '18 may be made of glass, butit may also be made of any other suitable material. Glass isparticularly desirable because it enables the user to determine quicklywhether or not the protector has opened the circuit. The end caps I2 andI4 may be made in any desired size and are of metal and serve as conacts between the protector and the circuit to be protected. In such acase, these end caps co .stitute the contact terminals of the protector.

Positioned within the enclosure, and secured in good electrical andthermal conducting relation with end cap I 2 by relatively high meltingpoint alloy i6, is a fusible heat generating element i 8. This element18 may, on overloads in the short circuit range, generate suillcientheat to fuse and thereby open the circuit. On overloads below the shortcircuit range, the element i8 will generate much less heat and will tendto retard heat flow from heat softenable material 22 to end cap i2,rather than to add heat to 22. Element I8 is shown in the drawing as aconductor in the form of a loop with its closed end extending into theenclosure ID. The closed end of element i 8 is held in electricalcontact with a member 20 by heat softenable material 22. This materialordinarily will be a low melting point solder or alloy, but any holdingmaterial that loses its holding power when heated to a predeterminedtemperature may be used. The member 28 may be made from any suitablematerial and of any suitable size, but is preferably made relativelylarge and is preferably made of metal.

A heat generating element 24 is wound on and supported by member 20 andis connected to the enlarged end of member 20 at the point 24; At thispoint the end of the element 24 extends through an opening in member 20and is held there by being bent over, and also by the fusible alloy 22.This element 24 is connected at its other end to end cap H by relativelyhigh melting point alloy IT. The wire 24 is. insulated from member 28except at the point indicated by the numeral 28; and at that point thereis good thermal and electrical contact between 24 and 28. Attached toone end of member 28 is a washer 28 that is made of insulating material.This washer may be attached to the member 20 by any suitable means butpreferably is attached by inserting member 28 through a hole in thewasher and then enlarging the end of member 20. A spring 30 is shown, inthe drawing, which has three different diameters. The smallest diameteris smaller than the external dimensions of the washer 28, the middlediameter is larger than the external dimensions of the washer 28 butslightly smaller than the internal diameter of tube 10, and the thirddiameter is larger than the internal diameter of tube to, but smallerthan the internal diameter of end cap l4. The washer28 is desirablebecause it insulates spring 30 from the heat absorbing member 20 whichmay become quite warm. Furthermore, the washer 28 frees spring In fromcurrent flow therethrough, and thereby obviates impairment of theresilient properties of the spring due to any electrical heatingthereof.

The end of the wire 24 that extends beyond washer 28 and is connected toend cap l4 must be relatively flexible because it must collapse when thecircuit is opened by movement of mem ber 28. Such an arrangement isentirely feasible because a relatively small wire can be used. The useof the end of wire 24 in place of a lead in wire is desirable because itkeeps down the number of parts and connections needed. Furthermore, theend of wire 24, between washer 28 and end cap I4, may also fuse onoverloads in the short circuit range. The wire 24 is not primarilyintended to fuse on overloads in the short circuit range and it is sodimensioned that it will not fuse until after the fuse link I 8 hasfused. Should the wire 24 fuse after the fusing of element l8, no harmwill result and in fact an unusually quick extinction of the arc may behad because of the formation of two arcing gaps in series.

The wire 24 is wound on and supported by the exterior surface of themember 28 and can thus radiate considerable heat into the atmosphere inthe enclosure. This radiation is quite desirable because it delays theheating of member 28, and therefore the heating of solder 22, by heater24. Such a delay is desirable because it gives more time lag to theprotector and thus prevents needless opening of the circuit. Thisradiation.

does not halt the heating of solder 22 and where the overload isprolonged unduly, the heater 24 wi l cause the solder 22 to soften andpermit the protector to open the circuit.

The drawing shows the fuse link It with two legs and a closed end. Thiskind of link is quite desirable because it can be held rather easily bythe heat softenable material 22 since the closed end enable the material22 to get a positive hold on the link. In large size protectors, thereis sumcient area of contact between the solder and the end of a straightlink to assure a permanent hold; but in the small sizes for which thisprotector is well adapted the diameter, and therefore the area, of thelink is quite small. Accordingly, it has been found desirable to providethe loop to guarantee a firm connection between the solder 22 and thelink II.

The provision or two legs for the link is also desirable because itpermits the link to burn quite readily when the circuit is opened onoverloads, and such burning rapidly increases the gap and quicklyextinguishes the arc. The mass of each leg of the link is considerablyless than the mass of an ordinary link of the same current carryingcapacity, and the legs of element l8 can therefore burn back much morereadily. In the present invention the two legs of the fuse link arefurther useful in affording support to the end of member 2|. Thissupport is particularly useful against movement in the plane of the twolegs of the link but it is also useful against movement in other planes.This construction of the link i| cooperates with the construction ofspring 30 to resiliently space element 20 away from the inner surface oftube i0. Such an arrangement is highly desirable in reducing thevibration imparted to the member 20 when the enclosure is subjected tovibration.

In automotive and aircraft work. protectors are often subjected to veryconsiderable vibration. If the parts were rigidly secured to theenclosure, the vibration imparted to the enclosure would immediately beimparted to the parts of the protector without diminution. Suchvibration might have serious results if it caused premature andaccidental opening of the protector. The arrangement shown in thedrawing is very helpin] in reducing the amount of vibration imparted tocertain parts of the protector, because much of the vibration impartedto the enclosure will be absorbed by the tensioned link i8 and by spring2| and only a very little of it will be imparted to member 2| and solder22. This insures that the life of the protector will not be shortened byinjuries caused by vibration.

This arrangementof parts is also helpful because it thermally insulateslink ll, heater wire 24 and heat absorber 2| from the tube l0. Spring 2|places link i2 and member 2| under tension and keeps H and 2| from sag ig to such an extent that they contact the inner surfaces of tube II.This is particularly desirable in the case of link i| because it will beheated and will expand. Such expansion cannot cause the link to sagagainst the enclosure because the spring will absorb the expansion andhold the link away from the enclosure. Spring 3| is additionally enabledto space member 2| away from the inner surfaces of tube l|. because themiddle diameter of the spring is preferably dimensioned so it is onlyslightly less than the inner diameter of the tube. As a result the smalldiameter of the spring, and the washer 2| and the end of member 2|supported by the mall diameter of the spring, are prevented from movingfrom the dis-metric center of the tube I I.

The wire 24 is insulated from member 2| except at the point 2|. Thedrawing shows the wire covered with insulation, and in practice a cottoncovered wire has been found to be very aw tory. However it is possibleto use other kinds of insulation on the wire 24, and it is also possibleto coat the external surface of member 2| with insulating material. Theinsulation that is used will electrically insulate the turns of the coilof wire 24 from each other and from member 2|, but it must not preventsubstantial heat flow from wire 24 to member 2|. Where cotton covered orenameled wire is used to insulate heater 24, the member 2| will absorbheat from the cotton or enamel insulation. This heat will be conductedto solder 22 and before the temperature of the insulation getsdangerously high. the solder will soften and permit the member 2| tomove and open the circuit.

In the preferred construction shown in the drawing, member 2| has arelatively large end to which fuse link I2 is soldered. This large endis not so large that it will not pass through the smallest diameter ofspring 3|, but it is preferably large enough to absorb an appreciableamount 01' the heat generated in the protector and thereby delay theheating of solder 22. Such a large end is also desirable because it willbe one of the arcing contacts of the protector and will readily absorbheat from the are generated when the protector opens. The large end ofmember 20 is further desirable because it can carry a considerablequantity of heat softenable material. Such a quantity of material notonly appreciably increases the time lag but also helps cool arcs thatmay form when the circuit is opened. If desired, the end of member 24can be formed in a cup-like shape to hold even more heat softenablematerial. Such a construction is shown in Fig. 3, and the additionalamount of heat softenable material held in the cup-like end will provideeven more time lag for the protector.

Member 2| and the portion of wire 24 supported on that member, as wellas material 22, are positioned in the approximate diametric andlongitudinal center of the enclosure. By this construction they are eachspaced away from the enclosure and at least partially insulated from theeffects of varying temperatures of the enclosure and the temperature ofthe clips to which the protector is secured. This arrangement isdesirable because it insures a uniform rating for the protector.

The positioning of members 2| and 24 in the longitudinal center of theenclosure is desirable for another reason. In fuses that are enclosed inglass tubes, it is sometimes dimcult to determine visually whether ornot the fuse is intact. This is largely due t the fact that the fusewires are generally quite small and is partially due to the fact thatthe e .d caps cover up a portion of the tube. with the arrangement shownin the drawing, these problems are not present because the members 2|and 24 constitute a thick mass that can be seen quite readily because itis large and it moves an appreciable distance when the circuit isopened. Such movement is an excellent index of the condition of theprotector, and facilitates ready detection of protectors that haveoperated to open the circuit.

The movement of the member 2| is not only useful in indicating thecondition of the protector, but is useful inbreaking the are. Whetherthe circuit opens by fusion of element i8 or fusion of solder 22, themember 20 will move. As it does so, it draws out any arc that may formuntil the arc breaks. This is done quickly and helps extinguish the arc.

Under ordinary conditions when the circuit is carrying a normal load,current will flow through end cap l2, through element i8, through a,short portion of member 20 into element 24, and cut end cap 14. Elementl8 and element 24 will generate some heat but will not cause solder 22to lose its holding power or cause element l8 to fuse. As a result, theprotector will carry such a load indefinitely.

If an overload occurs that is below the short circuit range but is soheavy that it would injure the circuit if prolonged unduly, the devicewill operate to open the circuit. Upon the occurrence of this type ofoverload, the element 24 will generate more heat than it does undernormal loads. The heat generated in element 24 will be conducted tosolder 22 through the wire itself and also through member 20. This flowof heat to solder 22 is not rapid because it takes time for the heatfrom the coil to heat the member 20 and the wire 24 that forms the coil.As a result there is an appreciable length of time that must elapsebefore the heating of wire 24 can cause the solder to lose its holdingpower.

The heating of wire 24 is primarily intended to raise the temperature ofsolder 22 to the point at which it loses its holding power, but theheating also acts to retard heat flow between solder 22 and end cap l4.In the absence of heater 24, differences between the temperature ofsolderi22 and end cap i4 would cause heat to flow between them. Suchheat flow would vary in response to temperature conditions of the endcap i4 and might be completely independent of the overload in thecircuit. This would be objectionable because it would cause undesirablevariations in the performance of the protector.

In much the same fashion, fuse link l8 retards and much of its heat isabsorbed and dissipated by end cap l2. As a result, it is the heat fromelement l8 instead of the heat from solder 22 that .is absorbed anddissipated by end cap I2. This arrangement minimizes variations in thetemperature of solder 22 in response to changes in the temperature ofend cap l2.

When, under the heating effect of wire 24, the heat softenable material22 loses its holding power the member 20 will be moved away from link l8by spring 30 and will open the circuit. In the event an arc formsbetween the ends of i8 and 20, it will be extinguished rather readily bycontinued movement of member 20, the cooling action of the large end ofmember 20, and the buming back of element IS. The burning back ofelement is is rapid because the use of two legs permits the mass of eachleg to be small and permits the legs to be consumed quite readily.

When however, an overload in the short circuit range occurs, the elementIt will become hot enough to cause one or both of its legs to fusealmost instantly. In the event only one leg of element It fusesinitially, the current will all flow assaoes through the other leg andwill be great enough to cause an immediate fusion of that leg. Wheresuch fusions occur, the arc will be extinguished rather rapidly becausethe member 20 will quickly 5 be moved away from the end of the elementi8 by the spring 30 in the manner explained above.

In the case described above where the overload causes the thermalcut-out to open the circuit, the overload must continue for apredetermined length of time. Where the overload is of short durationonly, the temperatures in the thermal cut-out will not be high enough tocause it to open the circuit, and this is desirable because it preventsneedless blowing of the protector.

This is well illustrated by the following table that is a. comparisonbetween the time lag of a simple fuse link and a protector of the samerating. The fuse link and the protector were each rated at one half ofan ampere and were tested at one hundred and thirty-five, one hundredand fifty, two hundred, three hundred, four hundred, five hundred, sixhundred, seven hundred, eight hundred, and nine hundred per cent loads.No entries are made for the fuse link above two hundred per cent loadbecause the opening times above that load were so short they could notbe measured with a stop-watch.

I In these (uses the link was touching the inner surface of the glassenclosure and that touching was materially disturbing the opening timeof the fuse.

The attainment of the above results is made possible by the use of theconstruction shown 4,5 in the drawing. In this construction, a fuse linkI! may be selected that will give the desired action on overloads in theshort circuit range; and when this has been done, the length andcharacter of the wire 24 is adjusted to give the desired action onoverloads below the short circuit range. By proper selection anddimensioning of the wire 24, it is possible to obtain the exact ratingdesired. It is desirable to rely on the wire 24 rather than fuse link l8for the determination of the rating, because the wire is much longer anda good portion of it is spaced a considerable distance from the endcaps. The sizeable length of Wire 24 is advantageous because a variationin the length of a long con- 0 ductor is not as noticeable as an equalvariation in the length of a short conductor such as fuse link l8.

Ti 2 length of wire 24 may be varied to change the time lag and ratingof the protector, but 'ther is a minimum length that must be pre served.For example, the developed length of the wire must be longer than theoverall length by a distance not less than six times the diameter of thewire 24, and in most cases will be considerably longer. With such aconstruction the overall length of the heater may be said to besubstantially smaller than its developed length.

In the preferred form shown in the drawin the heater 24 is coiled aroimdthe movable memher 20, but it need not be formed as a coil. In-

stead it may be bent into various shapes and conflsurations such ascrimps. crinkles, kinks, loops or other developable forms. In all cases.however, the developed length must be longer than the overall length bya distance not less than six times the diameter of the wire in theheater. 1'

The spacing of ,the coiled portion of wire 24 from the end cap. I: andI4 reduces the eilect that the end caps might have on the rating or theprotector. Therefore. the use of the portion of wire 24, between washer2! and end cap I4, and the fuse ink II to space the coiled portion orwire 24 away from the end caps is helpful in providing a uniformperformance of the protector. Such uniformity would not be possible ifi'use link It we rethe element that was used to determine the rating ofthe protector, because it is quite short and is intimately connectedwith the much more massive end cap 12. The relatively massive end cap I!will have quite an effect on the temperature of link I8 and if thetemperature of link il determined the rating or the protector, thetemperature of end cap I! would materially aifect the rating of theprotector. By avoiding such an occurrence, the present invention makespossible a better and more dependable protector.

In almost all cases, the temperature of theprotector will be less thanthat of the fuse link it replaces. This is the result of the use ofrelatively low melting point solder that melts considerably below thetemperature at which a fuse link fuses. In a simple iuse the temperaturemust reach the fusing point of the link before the circuit can beopened, whereas in the protector shown in the drawing the overalltemperature cannot rise above the melting point of the solder 22.

The protector shown in the drawing is presently being used in certainampere ratings to protect circuits up to two hundred and fifty volts.when such circuits are opened, there can be considerable arcing but theprotector shown in the drawing operates faultlessly despite the arcing.This is remarkable because the outside dimensions some of the enclosuresin which the protector is used are only one quarter of an inch by oneand one quarter inches.

While this invention is particularly desirable for use in very smallenclosures, it is not necessarily restricted to such enclosures. Themany desirable features of this invention may be used equally as well ondevices to be inserted in larger enclosures.

The invention makes it possible to position a protector in very smallenclosures by using a small number of parts ahdmaking some of the partsmovable. Furthermore several of the parts periorm dual functions. Forinstance in the protector shown in the drawing, the member 20 functionsas a heat absorber, an arcing contact and a movable support for theheater 2. The link it serves as a iuse link, serves as an arcing contactand serves as a support for the end of member 2|. The spring II also hasa dual function in that it serves to move member 20 longitudinally ofthe enclosure to open the circuit and it also serves to resilientlyspace member 20, wire 24 and element It away from the inner surfaces ofthe tube "I. This interaction of parts is desirable because it obviatesthe necessity of making each of the parts self-supporting, permits theparts to be made quite small, and eliminates the necessity of havingsupporting parts that might keep the protector from being positioned andoperated in a small enclosure.

The protector shown in the drawing can be assembled quite easily. Oneend of wire :4 is inserted in hole 20 in one end of member 2| and bentover and the wire is wound onto member 2|. The other end of member 20 isinserted in a hole in washer 2| and planished to prevent its withdrawal.The end of link it, the end of member 2| and the end of wire 24 are thensecured together by heat softenable material. Spring 30 is then slippedover the link II and member 20 until its small diameter engages washer2|. The assembly is then dropped into tube II and tensioned by pullingthe free ends of link it. The end caps are then put on and soldered toelements II and 24 and the free ends of ll are out on. This simplifiedprocedure is due in some measure to the use of the three di-' ameterspring 80. Such a spring is desirable because it obviates the use of apin or solder to secure it to the end cap I 4. The use of such a pin orsolder makes assembly more expensive and diflicult because the use 0! apin means the making and handling of a separate part and the use of thesolder is difficult because some spring materials are not solderedeasily.

Whereas a preferred embodiment oi the invention has been shown anddescribed in the drawing and accompanying description, it is obvious tothose skilled in the art that various changes in the form of theinvention may be made that do not aitect the scope of the invention.

What I claim is:

1. A protector for electric circuits that comprises contact terminals, amovable member, heat softenable material, a resilient member and aplurality of heat generating elements, at least one of which is fusibleon predetermined overload of the protector, another of said heat generating elements being arranged so the major portion thereof issupported on and coextensive with said movable member and a minorportion thereof extends from said movable member to one of said contactterminals and is permanently secured thereto, said heat softenablematerial normally maintaining an electrical conducting relation betweensaid heat generating elements and being arranged to permit aninterruption of said relation by said resilient member when heated to apredetermined temperature.

2. A protector for electric circuits that comprises contact terminals, aplurality of heat generating elements, at least one of which is adaptedto fuse and thereby open the circuit, another 0! said heat generatingelements having a developable major portion positioned relatively remotefrom said terminals and being arranged so heat flow between saidterminals and said major portion is retarded by heat in a minor portionof said other heat generating element that extends between said majorportion and one of said terminals and also by heat in said fusible heatgenerating element, heat softenable material that is positioned betweenand arranged to hold said heat generating elements in electricalconducting relation, and a resilient member arranged to move said majorportion and interrupt said relation when said heat softenable materialloses its holding power.

3. A protector for electric circuits that comprises contact terminals,heat softenable material spaced from said terminals, a plurality of heatgenerating elements, at least one of which is adapted to fuse andthereby open the circuit,

another of said heat generating elements having a portion thereof in theform of a coil that is arranged to add heat to said heat softenablematerial, and a second portion thereof extending from said coil portionto one of said ter. minals, and a resilient member, said fusible heatgenerating element and said second portion being arranged to generateheat and thus retard heat flow between said coil portion and saidterminals,

'said resilient member being arranged to move said coil portion of saidother heat generating element away from said fusible heat generatingelement when said heat softenable material has lost its holding power.

4. A protector for electric circuits that comprises contact terminals, aplurality of heat generating elements. at least one of which is adaptedto fuse and thereby open the circuit, heat softenable material normallyconnecting said heat generatin elements, a movable member and aresilient member, another of said heat generating elements having aportion thereof that is coextensive with a portion of said movablemember, said coextensive portions being fixedly spaced apart by anon-conductor of electricity, said resilient member being arranged tomove said movable member and break said connection when said heatsoftenable material has lost its holding power.

5. A protector for electric circuits that comprises an enclosure,contact terminals, a plurality of heat generating elements permanentlysecured to said terminals, at least one of said elements being adaptedto fuse and thereby open the-circuit. heat softenable material and aresilient member, said heat softenable material normally maintaining anelectrical conducting relation between said heat generating elements,said resilient member being arranged to be substantially free fromcurrent flow therethrough and to cooperate with said fusible heatgenerating element to space another of said heat generating elementsfrom the inner surface of said enclosure.

6. A protector for electric circuits that comprises an enclosure,contact terminals, a movable member, a plurality of heat generatingelements, at least one of which is adapted to fuse and thereby open thecircuit, a resilient member, another of said heat generating elementshaving a portion thereof supported on and coextensive with a portion ofthe exterior surface of said movable member, and means normally holdingsaid heat generating elements in electrical conducting relation, saidresilient member and said fusible heat generating element cooperating tospace said other heat generating element away from the inner surface ofsaid enclosure, whereby contact between said other element and saidenclosure is prevented and uniform rating of the protector is insured,said resilient member being arranged to move said movable member whensaid holding means has lost its holding power.

7. A protector for electric circuits that comprises an enclosure,contact terminals, a plurality of heat generating elements, at least oneof which is adapted to fuse and thereby open the circuit, a movablemember. a resilient member, and means normally holding said terminals inelectrical conducting relation, said resilient member being arranged tocooperate with said movable member and said fusible heat generatingelement to space another heat generating element from the inner surfaceof said enclosure without subjecting t". major portion of said otherheat generating element to tension and being arranged to move saidmovable member when said holding means has lost its holding power.

8. A protector for electric circuits that comprises contact terminals, atransparent enclosure, a plurality of heat generating elements, at leastone of which is adapted to fuse and thereby open the circuit, another ofwhich has a developable portion, heat softenable material, a movablemember that is positioned in said enclosure and supports saiddevelopable portion, said movable member and said developable portionconstituting a mass thicker than said fusible heat generating element,and a resilient member, said resilient member being arranged to movesaid movable member to open circuit position whenever said fusible heatgenerating element fuses or said heat softenable material loses itsholding power. said transparent enclosure permitting the position of thethick mass to indicate the condition of the protector.

9. A protector for electric circuits comprising contact terminals, aplurality of heat generating elements, at least one of said heatgenerating elements being adapted to fuse and thereby open the circuiton predetermined overload of the protector, a movable member, heatsoftenable material adjacent one end of said movable member normallycontacting each of said heat generatin elements whereby said heatgenerating elements are held in thermal and electrical lation, and aresilient member biasing said movable member for movement whenever saidheat softenable material loses its holding power or said fusible heatgenerating element fuses.

10. A protector for electric circuits comprising a plurality of heatgenerating elements, at least one of said heat generating elements beingadapted to fuse and thereby open the circuit on predetermined overloadof the protector, a movable mem ber constructed and arranged to supportand carry a portion of another of said heat generating elements, heatsoftenable material on said movable member normally contacting each ofsaid heat generating elements to hold them in thermal and electricalconducting relation, and a resilient member biasing said movable memberand said portion of said other heat generating element for movement awayfrom said fusible heat generating element to open the circuit wheneversaid heat softenable material loses its holding power.

11. A protector for electric circuits that comprises a plurality of heatgenerating elements, at least one of which is adapted to fuse andthereby open the circuit, another of said heat generating elementshaving a portion whose overall length is substantially smaller than itsdeveloped length, heat softenable material normally holding said headgenerating elements in electrical conducting relation, and a resilientmember that is operable to move said portion of said other heatgenerating element and interrupt said electrical conducting relationwhenever said heat softenable material loses its holding power.

12. A protector for electric circuits that comprises contact terminals,a plurality of heat generating elements, at least one of which isadapted to fuse and thereby open the circuit, another of said heatgenerating elements having a developable portion whose overall length issubstantially smaller than its developed length and having a secondportion extending from said developable portion to one of saidterminals, heat softenable conducting rematerial normally holding saidheat generating elements in electrical conducting relation, and aresilient member that is operable to move said developable portion ofsaid element and interrupt said electrical conducting relation wheneversaid heat softenable material loses its holding power, said fusible heatgenerating element and said second portion of said other heat generatingelement being arranged to generate heat and thus retard heat flowbetween said developable portion and said terminals.

13. A protector for electric circuits that comprises an enclosure,contact terminals, a plurality of heat generating elements, at least oneof which is adapted to fuse and thereby open the circuit. heatsoftenable material normally holding said heat generating elements inelectrical conducting relation, and a resilient member that is operableto move a portion of another of said heat generating elements and tointerrupt said electrical conducting relation whenever said heatsoftenable material loses its holding power, said resilient member beingarranged to resiliently space said fusible heat generating element, heatsoftenable material and other heat generating element away from theinner surface of said enclosure.

14. A protector for electric circuits that comprises a contact terminal,a heat generating element that is permanently secured to said terminaland has a portion whose overall length is substantially smaller than itsdeveloped length, heat softenable material, a member associated andmovable with said portion of said heat generating element that isarranged to absorb an appreciable portion of the heat generated in theprotector, and

a resilient member that is operable to move said portion of said heatgenerating element and said movable member to open the circuit wheneversaid heat softenable material has been heated to a predetermined temrature.

15. A protector for electric circuits that comprises a heat generatingelement having a portion whose overall length is substantially smallerthan its developed length, heat softenable material, a normallystationary member arranged to absorb an appreciable portion of the heatgenerated in said protector and to be moved whenever the protectoroperates to open the circuit, and a resilient member that is operable tomove said normally stationary member whenever the protector opens thecircuit.

16. A protector for electric circuits that comprises an enclosure,contact terminals, a fusible heat generating element, heat softenablematerial, a movable heat absorbing member having outside dimensionsappreciably smaller than the inner dimensions of said enclosure, and aresilient member substantially free from current flow therethrough thatis arranged to exert a tension in said movable member and in said heatgenerating element longitudinally of said enclosure whereby said movablemember will remain resiliently spaced away from the inner surface of sid enclosure regardless of any expansion of said fusible heat generatingelement and will be moved to open circuit position when said heatsoftenable material has been heated to a predetermined temperature, saidfusible heat genrating element remaining in substantially fixed positionwhen said movable member is moved.

1?. A protector for electric circuits comprisin a plurality of heatgenerating elements, at least one of said heat generating elements beinadapted to fuse and thereby open the circuit on predetermined overloadof the protector, a movable member. heat softenable material in directcontact with a portion of said movable member and a portion of each ofsaid heat generating elements that normally maintains said elements incurrent conducting relation, another of said heat generating elementsbeing arranged to heat said material directly by thermal conduction atsaid contact and indirectly by heating said movable member, and aresilient member arranged to move said movable member and a portion ofsaid other heat generating element out of electrical connection withsaid fusible heat generating element to open the circuit whenever saidheat softenable material loses its holding power.

18. A protector for electric circuits comprising contact terminals, aplurality of heat generating elements, at least one of said heatgenerating elements being adapted to fuse and thereby open the circuiton predetermined overload of the protector, a movable member, another ofsaid heat generating elements having the major portion thereofcoextensive with a portion of said movable member whereby said movablemember can absorb an appreciable portion of the heat generated by saidother heat generating element and can conduct said absorbed heat to oneend of the movable member, heat softenable material adjacent said end ofsaid movable member normally contacting each of said heat generatingelements and thereby holding them in thermal and electrical conductingrelation, and a resilient member biasing said movable member formovement to break said relation and thereby open the circuit when-saidheat softenable material has lost its holding power.

19. A protector for electric circuits comprising a plurality of heatgenerating elements, at least one of said heat generating elements beingadapted to fuse and thereby open the circuit on predetermined overloadof the protector, a movable member constructed and arranged to carryanother of said heat generating elements, a resilient member biasingsaid movable member to open circuit position, and heat softenablematerial that normally directly contacts each of said heat generatingelements and is arranged to be heated on certain overloads of theprotector to permit said movable member to move to open circuitposition.

20. A protector for electric circuits comprising a plurality of heatgenerating elements, at least one of said' heat generating elementsbeing adapted to fuse and thereby open the circuit on predeterminedoverload of the protector, a movable member and another of said heatgenerating elements that are arranged for concurrent movement, a portionof said other heat generating element being coextensive with but spacedfrom a portion of said movable member by a nonconductor of electricity,heat softenable material normally connecting said other heat generatingelement and said movable member with said fusible heat generatingelement, and a resilient member biasing said movable member and saidother heat generating element for movement away mom said fusible heatgenerating element to break said connection and thereby open the circuitwhen said heat softenable material has lost its holding power.

21. A protector for electric circuits that comprises a plurality of heatgenerating elements at least one of which is adapted to fuse and therebyopen the circuit on predetermined overload of the protector, a movablemember, another of said heat generating elements having the majorportion thereof coextensive with a portion of said movable member andbeing supported on and carried by said movable member, said other heatgenerating element being arranged so at least a portion thereof willflex upon movement of said movable member, heat softenable materialnormally maintaining said heat generating elements in electricalconducting relation, and a resilient member biasing said movable memberand said major portion of said other heat generating element formovement to open circuit position when said heat softenable materialloses its holding power.

22. A protector for electric circuits that comprises a plurality of heatgenerating elements, one of said elements being relatively short andbeing adapted to fuse on predetermined overloads of the protector, aplurality of contact terminals that are each massive relative to saidfusible heat generating element, another of said heat generatingelements being flexible and being relatively long, said fusible heatgenerating element being positioned adjacent to and in good electricaland thermal connection with one of said contact terminals whereby themajor portion of the heat generated by said fusible heat generatingelement is absorbed by said terminal, heat softenable material normallymaintaining said heat generating elements in electrical conductingrelation, said elements being arranged so heating of said material atcertain overloads is mainly due to the heating of said other heatgenerating element, and resilient means arranged to movesaid other heatgenerating element whenever the protector opens the circuit.

23. A protector for electric circuits that comprises an enclosure,contact terminals, a movable member, heat softenable material, aresilient member and a plurality of heat generating elements, at leastone of which is adapted to fuse, another of said heat generatingelements being arranged so the major portion thereof is supported on andcoextensive with a portion of said movable member, said resilient memberand said fusible heat generating element cooperating to space said heatsoftenable material and said major portion of said other heat generatingelement away from the inner surface of said enclosure, said heatsoftenable material normally maintaining said fusible heat generatingelement and said other heat generating element in electrical conductingrelation and being arranged, when heated to a predetermined temperature,to permit an interruption of said relation by movement of said otherheat generating element away from said fusible heat generating element.

24. A protector for electric circuits comprising a movable member, heatsoftenable material, and a plurality of heat generating elements, atleast one of which is adapted to fuse and thereby open the circuit,another of said heat generating elements being arranged so the majorportion thereof is supported on and coextensive with said movablemember, said movable member being constructed and arranged to aborb anappreciable portion of the heat generated in the protector. heatsoftenable material adjacent one end of said movable member normallycontacting each of said seat generating elements to maintain them inelectrical conducting relation and being arranged to permit movement ofthe movable member and consequent opening of the circuit when heated toa predetermined temperature.

25. A protector for electric circuits that comprises an enclosure,contact terminals, heat softenable material, a movable member, aplurality of heat generating elements, at least one of which is adaptedto fuse and thereby open the circuit, and a resilient member, said heatsoftenable material being positioned adjacent one end of said movablemember and normally contacting each of said heat generating elements andthereby maintaining them in thermal and electrical conducting relation,said resilient member and said fusible heat generating elementcooperating to space said heat softenable material, movable member andanother of said heat generating elements away from the inner surface ofsaid enclosure. said resilient member biasing said movable member formovement whenever said heat softenable material loses its holding poweror said fuse link fuses.

26. A protector for electric circuits that comprises an enclosure,contact terminals, a movable member, heat softenable material, aresilient member and a plurality of heat generating elements, at leastone of which is adapted to fuse and thereby open the circuit, another ofsaid heat generating elements being arranged so the major portionthereof is supported on and coextensive with said movable member, saidheat softenable material being positioned adjacent one end of saidmovable member and normally contacting each of said heat generatingelements and thereby maintaining them in thermal and electricalconducting relation, said resilient member blasing said movable memberfor movement to open circuit position whenever said heat softenablematerial loses its holding power, said resilient member and said fusibleheat generating element cooperating to resiliently space said heatsoftenable material and said movable member away from the inner surfaceof said enclosure.

27. A protector for electric circuits that comprises heat softenablematerial, a plurality of heat generating elements, at least one of whichis adapted to fuse and thereby open the circuit, another of said heatgenerating elements having a portion whose overall length issubstantially smaller than its developed length, a movable memberarranged so said portion of said heat generating element is supported onand coextensive with said movable member, said heat softenable materialnormally maintaining said heat generating elements in electricalconducting relation, said resilient member being operable to move saidportion of said element and said movable member to interrupt saidrelation whenever said heat softenable material loses its holding power.

28. A protector for electric circuits that comprises an enclosure,contact terminals, heat softenable material, a plurality of heatgenerating elements, at least one of which is adapted to fuse andthereby open the circuit, a movable member and a resilient member, saidresilient member cooperating with said fusible heat generating elementto resiliently space said heat softenable material and said movablemember away from the inner surface of said enclosure, another of saidheat generating elements having a portion whose overall length issubstantially smaller than its developed length, said movable member andsaid portion of said heat generating element being arranged so saidportion is free from stress due to said resilient member and beingnormally held in closed circuit position by said heat softenablematerial and being arranged to be moved to open circuit position by saidresilient member whenever said heat softenable material loses itsholding power.

29. A protector for electric circuits comprising a plurality of heatgenerating elements, at least one of which is adapted to fuse andthereby open the circuit, another of said heat generating elementshaving a portion whos overall length is substantially smaller than itsdeveloped length, a movable member constructed and arranged to supportsaid portion of said heat generating element and to absorb anappreciable portion of the heat generated in the protector, heatsoftenable material adjacent one end of said movable member normallycontacting each of said heat generating elements and thereby maintainingthem in thermal and electrical conducting relation, said resilientmember biasing said movable member and said portion of said heatgenerating element for movement out of electrical contact with saidfusible heat generating element to open the circuit whenever said heatsoftenable material loses its holding power.

30. A protector for electric circuits comprising a movable member, heatsoftenable material, a resilient member, and a plurality of heatgenerating elements, at least one of which is adapted to fuse andthereby open the circuit, another of said heat generating elementshaving a portion whose overall length is substantially smaller than itsdeveloped length, said movable member being constructed and arranged tobe coextensive with and to support said portion of said heat generatingelement and to absorb an appreciable amount of the heat generated in theprotector, said heat softenable material normally contacting each ofsaid heat generating elements and thereby maintaining them in thermaland electrical conducting relation, said resilient member being operableto move said portion of said heat generating element and said movablemember whenever said heat softenable material loses its holding power.

31. A protector for electric circuits that comprise an enclosure,contact terminals, a plurality a: heat generating elements, at least oneof which is adapted to fuse and thereby open the circuit, heatsoftenable material, a movable member havmg outside dimensionsappreciably smaller than the inner dimensions of said enclosure, and aresilient member that is normally arranged to exert a tension in saidmovable member and said fusible heat generating element longitudinal ofsaid enclosure without subjecting another of said heat generatingelements to tension, whereby said movable member and said heatsoftenable material will remain resiliently spaced away from the innersurfaces of said enclosure regardless of any expansion of said fusibleheat generating element, said other heat generating element beingarranged so the major portion thereof is supported on and is coextensivewith a portion of said movable member.

32. A protector for electric circuits that comprises an enclosure.contact terminals, heat sof tenable material, a movable member, aplurality of heat generating elements normally held in electricalconducting relation by said heat softenable material and at least one ofwhi'h is adapted to fuse and thereby open the circuit, and a, resiilentmember, said movable member having outside dimensions appreciablysmaller than the inner dimensions of said enclosure, said resilientmember being substantially free from current flow therethrough andarranged to exert a tension on said movable member and on said fusibleheat generating element longitudinally of said enclosure whereby saidmovable member and said heat softenable material will remain resilientlyspaced away from the inner surface of said enclosure regardless of anyexpansion of said fusible heat generating element, said fusible heatgenerating element being arranged to remain in substantially fixedposition when said movable memberismoved.

33. A protector for electric circuits comprising an enclosure, contactterminals, a plurality of heat generating elements, at least one ofwhich is adapted to fuse and thereby open the circuit, a movable memberand a resilient member, said movable member being constructed andarranged to absorb an appreciable portion of the heat generated in theprotector, said heat softenable material being positioned adjacent oneend of said movable member and normally contacting each of said heatgenerating elements and thereby maintaining them in thermal andelectrical conducting relation, said resilient member being arranged toexert a tension in said movable member and in said fusible heatgenerating element longitudinally of said enclosure whereby said movablemember and said heat softenable material will remain resiliently spacedaway from the inner surfaces of said enclosure regardles of anyexpansion of said fusible heat generating element, said resilient memberbiasing said movable member for movement away from said fusible heatgenerating element to open the circuit whenever said heat softenablematerial loses its holding power.

34. A protector for electric circuits that comprises an enclosure,contact terminals, a plurality of heat generating elements, at least oneof which is adapted to fuse and thereby open the circuit, heatsoftenable material, a movable member and a resilient member, another ofsaid heat generating elements having a portion whose overall length issubstantially smaller than its developed length, said movable memberhaving outside dimensions appreciably smaller than the inner dimensionsof said enclosure and being arranged to carry said portion of said heatgenerating element, heat softenable material normally contacting each ofsaid heat generating elements and thereby maintaining them in thermaland electrical conducting relation, said resilient member being arrangedto exert a tension in said movable member and said fusible heatgenerating element longitudinal of said enclosure whereby said movablemember and said heat softenable material will remain resiliently spacedaway from the inner surface of said enclosure regardless of anyexpansion of said fusible heat generating element and whereby saidmovable member will be moved away from said fusible heat generatingelement when said heat softenable material is heated to a predeterminedtemperature.

35. A protector for electric circuits that comprises an enclosure,contact terminals, a plurality of heat generating elements, at least oneof which is adapted to fuse and thereby open the circuit, heatsoftenable material, a movable member and a resilient member, another ofsaid heat generating elements being arranged so the major portionthereof is supported on and coextensive with a portion of said movablemember, said movable member having outside dimensions appreciablysmaller than the inner dimensions of said enclosure and being arrangedto absorb an appreciable portion of the-heat generated in the protector,said heat softenable material being adjacent one end of said movablemember and normally contacting each of said heat generating elements andthereby maintaining them in thermal and electrical conducting relation,said resilient member being arranged to exert a tension in said movablemember and said fusible heat generating element longitudinally of saidenclosure and to move said movable member whenever the protector opensthe circuit.

36. A protector for electric circuits that comprises an enclosure;contact terminals. a plurality of heat generating elements. at least oneof which is adapted to fuse and thereby open the circuit, heatsoftenable material, a movable member and a resilient member, another ofsaid eat generating elements having a portion whose overall length issubstantially smaller than its developed length. said movable memberhaving outside dimensions a preciably smaller than the inner dimensionsof said enclosure and being arranged to support said orti n of said heatgenerating element and to absorb an appreciable portion of the heatgenerated in said protector. said heat softenable material normally mantaining an electrical conducting relation between said heat generatinelements. said resilient member being arranged to exert a tension insaid movable member and said fusible heat generating element longituinally of said enclosure and to move said movable member and flex asecond portion of said other heat generating element.

37. A protector for electric circuits that comprises contact terminals,a movable member, a resilient member and a plurality of heat generatingelements. at least one of which is ada ted to fuse and thereby open thecircuit. heat softenable material normally connecting said heatgenerating elements. another of said heat generating elements beingarranged so the major portion thereof is sup orted on and coextensivewith a portion of said movable member and a minor portion thereofextends from said movable member to one of said contact terminals and ispermanently secured thereto, said resilient member being operable tomove said major portion of said other heat generating element away fromsaid fusible heat generating element and to open the circuit when saidheat softenable material has been heated to a predetermined temperature.

38. A protector for electric circuits that comprises a movable member,heat softenable material, and an electrical conductor, said conductorbeing arranged so the major portion thereof is supported on andcoextensive with a portion of said movable member, and means operable tomove said movable member whenever the protector opens the circuit.

39. A protector for electric circuits that comprises a contact terminal,heat softenable material, a heat generating element that is permanentlysecured to said terminal and has a portion thereof in the form of a coilthat is arranged to add heat to said heat softenable material, and aresil ent member, said resilient member being arranged to move said coilportion of said heat gener' ting element toward said terminal when saidheat softenable material has lost its holding power.

40. A protector for electric circuits comprising a plurality of heatgenerating elements, at least one of which is adapted to fuse andthereby open the circuit, a resilient member and heat softenablematerial, another of said heat generating elements having a developableportion arranged to be moved by said resilient member to open circuitposition when said heat softenable material reaches a predeterminedtempermining in substantially fixed position when said portion is moved,said developable portion and said heat softenable material and saidfusible heat generating element being arranged so heating of said heatsoftenable material at certain overloads is mainly due to heat from saiddevelopable portion.

41. In a protector for electric circuits, an enclosure, a movable memberand a coiled resilient member, said resilient member having at least oneexternal dimension closely approximating one interior dimension of saidenclosure, said resilient member being arranged to support at least oneend of said movable member, said dimensioning of said resilient memberbeing arranged to resiliently space said end of said movable member awayfrom the inner surfaces of said enclosure.

42. A protector for electric circuits that comprises a heat generatingelement, heat softenable material, a resilient member, and a movablemember, said heat generating element having a portion spaced away fromsaid movable member by a non-conductor of electricity, said portion ofsaid heat generating element being supported on and coextensive with aportion of said movable member, said non-conductor of electricity beingin contact with said portion of said heating element and with saidportion of movable member, said movable member being arranged to absorbheat from said non-conductor and to conduct said heat to said heatsoftenable material, said resilient member being arranged to move saidmovable member whenever the protector opens the circuit, said heatgenerating element and movable member and heat softenable material beingarranged so the protector will open the circuit before saidnon-conductor of electricity is injured by heat from said heatgenerating element.

43. In a protector for electric circuits, an enclosure, an end cap forsaid enclosure, a movable member and a helical resilient member, saidend cap having an internal diameter greater than the external diameterof said enclosure, said resilient member having a plurality ofdiameters, one of which diameters is smaller than the internal diameterof said enclosure and another is larger than the internal diameter ofthe enclosure but smaller than the internal diameter of the end capwhereby said resilient member can be held in assembled relation withsaid enclosure by said end cap.

44. In a protector for electric circuits, an enclosure, a fusibleconductor, heat softenable material and a movable member, said fusibleconductor being bent to form a U and being posi tioned in said enclosureso the closed end of the U extends inwardly of said enclosure, saidclosed end of said fusible conductor normally engaging and being securedto said movable member by said heat softenable material, said closed endof said fusible conductor providing a good hold for said heat softenablematerial whereby separation of said fusible conductor and said movablemember is prevented until the heat softenable material reaches apredetermined temperature.

45. In a protector for electric circuits, a heat generating element, amovable member that is arranged to be heated by said heat generatingelement, a resilient member and a member of insulating material arrangedto thermally insulate said resilient member from said movable member.

46. A protector for electric circuits that comature, said fusible heatgenerating element reprises Contact terminals. a pl rali y of heat 8erating elements, at least one of said elements being adapted to fuse onpredetermined overload of the protector, heat softenable material, amovable member and a resilient member, another of said heat generatingelements having 2. developable portion supported on and coextensive witha portion of said movable member, said movable member and said p01 tionof said heat generating element being spaced from said terminals, saidheat softenable material normally contacting each of said heatgenerating elements to hold them in electrical conducting relation, saidresilient member being arranged to move said portion of said heatgenerating element and said movable member away from said fusible heatgenerating element to interrupt said relation whenever said heatsoftenable material loses its holding power.

47. A protector for electric circuits comprising an enclosure, aplurality of heat generating elements, a movable member, heat softenablematerial and a resilient member, said heat generating elements havingtheir inner ends in proximity to each other and normally secured to oneend of said movable member by said heat softenable material, saidresilient member biasing said movable member for circuit openingmovement when said heat softenable material has been heated to apredetermined temperature.

48. A protector for electric circuits comprising a supporting member, aflexible conducting member having the major portion thereof supported onand coextensive with a portion of said supporting member, heatsoftenable material, and means operable to move at least one portion ofone of said members to open the circuit and to flex a portion of saidconducting member when said heat softenable material has been heated toa. predetermined temperature.

49. A protector for electric circuits comprising a supporting member, aiiexible conducting member having the major portion thereof supported onand coextensive with a portion of said supporting member, heatsoftenable material, and means operable to move one of said members andthereby open the circuit when said heat softenable material has beenheated to a predetermined temperature, said flexible conducting memberbeing substantially free from stress due to said opening means at alltimes when the circuit through the protector is closed.

50. A protector for electric circuits that comprises contact terminals,a heat generating element having a portion whose overall length issubstantially smaller than its developed length and another portionpermanently secured to one of said contact terminals, heat softenablematerial and a resilient member substantially free from current flowtherethrough that is operable to move said portion of said heatgenerating element and open the circuit whenever said heat softenablematerial is heated to a predetermined temperature.

51. A protector for electric circuits comprising an enclosure, aplurality of heat generating elements, a movable member, heat softenablematerial and a resilient member, said heat generating elements havingtheir inner ends in proximity to each other and secured to said movablemember adjacent one end thereof, one of said heat generating elementsbeing secured to said movable member by said heat soitenable material,said resilient member biasing said movable member for movement away fromsaid one heat generating element when the heat softenable material hasbeen heated to a predetermined temperature.

52. In a, protector for electric circuits 9. heat generating element, anenclosure, a resilient member having a relatively large portion thereofpositioned in close proximity to said enclosure whereby heating of saidresilient member is retarded by heat transfer between said resilientmember and said enclosure.

MANFRED 1'. DUERKOB.

